This study determined the effect of caffeine on peak torque, total work, and work fatigue in caffeine consumers. Active men (N = 7) refrained from intense exercise as well as alcohol and caffeine consumption 48 hours prior to each trial. Caffeine anhydrase dissolved in Crystal Light and water was ingested 70 minutes pre-trial. Trials with three different doses (2 mg/kg, 5 mg/kg, and placebo) were separated by one week. Exercise consisted of two sets of 40 repetitions of knee extension and flexion at 180 deg/s on an isokinetic dynamometer, with a 3-minute rest period between sets.

From bout 1 to bout 2, peak knee extension torque declined in all treatments. Across all treatments, total work of the knee extensors declined by approximately 20-30 %, and work fatigue increased from bout 1 to bout 2. Similar findings were revealed for the knee flexors. There was no effect of caffeine on any measure of muscular performance.

Implication. Low or high doses of caffeine have no effect on peak torque production, total work, or work fatigue of the knee extensors and flexors. Acute caffeine ingestion is unlikely to alter muscle endurance in resistance-trained men who regularly consume caffeine.